@aws/dynamodb-query-iterator
v0.7.1
Published
Abstraction for DynamoDB queries and scans that handles pagination and parallel worker coordination
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Amazon DynamoDB Query and Scan Iteration
This library provides utilities for automatically iterating over all DynamoDB records returned by a query or scan operation using async iterables. Each iterator and paginator included in this package automatically tracks DynamoDB metadata and supports resuming iteration from any point within a full query or scan.
Paginators
Paginators are asynchronous iterables that yield each page of results returned
by a DynamoDB query
or scan
operation. For sequential paginators, each
invocation of the next
method corresponds to an invocation of the underlying
API operation until all no more pages are available.
QueryPaginator
Retrieves all pages of a DynamoDB query
in order.
Example usage
import { QueryPaginator } from '@aws/dynamodb-query-iterator';
import DynamoDB = require('aws-sdk/clients/dynamodb');
const paginator = new QueryPaginator(
new DynamoDB({region: 'us-west-2'}),
{
TableName: 'my_table',
KeyConditionExpression: 'partitionKey = :value',
ExpressionAttributeValues: {
':value': {S: 'foo'}
},
ReturnConsumedCapacity: 'INDEXES'
}
);
for await (const page of paginator) {
// do something with `page`
}
// Inspect the total number of items yielded
console.log(paginator.count);
// Inspect the total number of items scanned by this operation
console.log(paginator.scannedCount);
// Inspect the capacity consumed by this operation
// This will only be available if `ReturnConsumedCapacity` was set on the input
console.log(paginator.consumedCapacity);
Suspending and resuming queries
You can suspend any running query from within the for
loop by using the
break
keyword. If there are still pages that have not been fetched, the
lastEvaluatedKey
property of paginator will be defined. This can be provided
as the ExclusiveStartKey
for another QueryPaginator
instance:
import { QueryPaginator } from '@aws/dynamodb-query-iterator';
import { QueryInput } from 'aws-sdk/clients/dynamodb';
import DynamoDB = require('aws-sdk/clients/dynamodb');
const dynamoDb = new DynamoDB({region: 'us-west-2'});
const input: QueryInput = {
TableName: 'my_table',
KeyConditionExpression: 'partitionKey = :value',
ExpressionAttributeValues: {
':value': {S: 'foo'}
},
ReturnConsumedCapacity: 'INDEXES'
};
const paginator = new QueryPaginator(dynamoDb, input);
for await (const page of paginator) {
// do something with the first page of results
break
}
for await (const page of new QueryPaginator(dynamoDb, {
...input,
ExclusiveStartKey: paginator.lastEvaluatedKey
})) {
// do something with the remaining pages
}
Suspending and resuming the same paginator instance is not supported.
ScanPaginator
Retrieves all pages of a DynamoDB scan
in order.
Example usage
import { ScanPaginator } from '@aws/dynamodb-query-iterator';
import DynamoDB = require('aws-sdk/clients/dynamodb');
const paginator = new ScanPaginator(
new DynamoDB({region: 'us-west-2'}),
{
TableName: 'my_table',
ReturnConsumedCapacity: 'INDEXES'
}
);
for await (const page of paginator) {
// do something with `page`
}
// Inspect the total number of items yielded
console.log(paginator.count);
// Inspect the total number of items scanned by this operation
console.log(paginator.scannedCount);
// Inspect the capacity consumed by this operation
// This will only be available if `ReturnConsumedCapacity` was set on the input
console.log(paginator.consumedCapacity);
Suspending and resuming scans
You can suspend any running scan from within the for
loop by using the break
keyword. If there are still pages that have not been fetched, the
lastEvaluatedKey
property of paginator will be defined. This can be provided
as the ExclusiveStartKey
for another ScanPaginator
instance:
import { ScanPaginator } from '@aws/dynamodb-query-iterator';
import { ScanInput } from 'aws-sdk/clients/dynamodb';
import DynamoDB = require('aws-sdk/clients/dynamodb');
const dynamoDb = new DynamoDB({region: 'us-west-2'});
const input: ScanInput = {
TableName: 'my_table',
ReturnConsumedCapacity: 'INDEXES'
};
const paginator = new ScanPaginator(dynamoDb, input);
for await (const page of paginator) {
// do something with the first page of results
break
}
for await (const page of new ScanPaginator(dynamoDb, {
...input,
ExclusiveStartKey: paginator.lastEvaluatedKey
})) {
// do something with the remaining pages
}
Suspending and resuming the same paginator instance is not supported.
ParallelScanPaginator
Retrieves all pages of a DynamoDB scan
utilizing a configurable number of scan
segments that operate in parallel. When performing a parallel scan, you must
specify the total number of segments you wish to use, and neither an
ExclusiveStartKey
nor a Segment
identifier may be included with the input
provided.
Example usage
import { ParallelScanPaginator } from '@aws/dynamodb-query-iterator';
import DynamoDB = require('aws-sdk/clients/dynamodb');
const paginator = new ParallelScanPaginator(
new DynamoDB({region: 'us-west-2'}),
{
TableName: 'my_table',
TotalSegments: 4,
ReturnConsumedCapacity: 'INDEXES'
}
);
for await (const page of paginator) {
// do something with `page`
}
// Inspect the total number of items yielded
console.log(paginator.count);
// Inspect the total number of items scanned by this operation
console.log(paginator.scannedCount);
// Inspect the capacity consumed by this operation
// This will only be available if `ReturnConsumedCapacity` was set on the input
console.log(paginator.consumedCapacity);
Suspending and resuming parallel scans
You can suspend any running scan from within the for
loop by using the break
keyword. If there are still pages that have not been fetched, the scanState
property of interrupted paginator can be provided to the constructor of another
ParallelScanPaginator
instance:
import {
ParallelScanInput,
ParallelScanPaginator,
} from '@aws/dynamodb-query-iterator';
import DynamoDB = require('aws-sdk/clients/dynamodb');
const client = new DynamoDB({region: 'us-west-2'});
const input: ParallelScanInput = {
TableName: 'my_table',
TotalSegments: 4,
ReturnConsumedCapacity: 'INDEXES'
};
const paginator = new ParallelScanPaginator(client, input);
for await (const page of paginator) {
// do something with the first page of results
break
}
for await (const page of new ParallelScanPaginator(
client,
input,
paginator.scanState
)) {
// do something with the remaining pages
}
Suspending and resuming the same paginator instance is not supported.
Iterators
Iterators are asynchronous iterables that yield each of record returned by a
DynamoDB query
or scan
operation. Each invocation of the next
method may
invoke the underlying API operation until all no more pages are available.
QueryIterator
Retrieves all records of a DynamoDB query
in order.
Example usage
import { QueryIterator } from '@aws/dynamodb-query-iterator';
import DynamoDB = require('aws-sdk/clients/dynamodb');
const iterator = new QueryIterator(
new DynamoDB({region: 'us-west-2'}),
{
TableName: 'my_table',
KeyConditionExpression: 'partitionKey = :value',
ExpressionAttributeValues: {
':value': {S: 'foo'}
},
ReturnConsumedCapacity: 'INDEXES'
},
['partitionKey']
);
for await (const record of iterator) {
// do something with `record`
}
// Inspect the total number of items yielded
console.log(iterator.count);
// Inspect the total number of items scanned by this operation
console.log(iterator.scannedCount);
// Inspect the capacity consumed by this operation
// This will only be available if `ReturnConsumedCapacity` was set on the input
console.log(iterator.consumedCapacity);
ScanIterator
Retrieves all records of a DynamoDB scan
in order.
Example usage
import { ScanIterator } from '@aws/dynamodb-query-iterator';
import DynamoDB = require('aws-sdk/clients/dynamodb');
const iterator = new ScanIterator(
new DynamoDB({region: 'us-west-2'}),
{
TableName: 'my_table',
ReturnConsumedCapacity: 'INDEXES'
},
['partitionKey', 'sortKey']
);
for await (const record of iterator) {
// do something with `record`
}
// Inspect the total number of items yielded
console.log(iterator.count);
// Inspect the total number of items scanned by this operation
console.log(iterator.scannedCount);
// Inspect the capacity consumed by this operation
// This will only be available if `ReturnConsumedCapacity` was set on the input
console.log(iterator.consumedCapacity);
ParallelScanIterator
Retrieves all pages of a DynamoDB scan
utilizing a configurable number of scan
segments that operate in parallel. When performing a parallel scan, you must
specify the total number of segments you wish to use, and neither an
ExclusiveStartKey
nor a Segment
identifier may be included with the input
provided.
Example usage
import { ParallelScanIterator} from '@aws/dynamodb-query-iterator';
import DynamoDB = require('aws-sdk/clients/dynamodb');
const iterator = new ParallelScanIterator(
new DynamoDB({region: 'us-west-2'}),
{
TableName: 'my_table',
TotalSegments: 4,
ReturnConsumedCapacity: 'INDEXES'
},
['partitionKey']
);
for await (const record of iterator) {
// do something with `record`
}
// Inspect the total number of items yielded
console.log(iterator.count);
// Inspect the total number of items scanned by this operation
console.log(iterator.scannedCount);
// Inspect the capacity consumed by this operation
// This will only be available if `ReturnConsumedCapacity` was set on the input
console.log(iterator.consumedCapacity);